To transmit torque between a rotor and an element to be driven by the rotor, switchable friction couplings are known with which parts to be coupled together, such as disk-like clutch components, can be optionally separated or connected together by friction or force fit.
Such friction switch couplings e.g. with a friction disk clutch can be formed as magnetic couplings which comprise an electromagnet arrangement with a coil body which can be electrically powered, e.g. a wire winding and coil carrier of magnetically conductive material.
These also include arrangements which in addition comprise permanent magnets, by the magnetic effect of which, when the electric magnets are not powered or not magnetically active, a movable coupling or armature element is attracted against the effect, e.g. a spring force, onto a counter segment and these are connected by force fit for torque transmission. When the electromagnet is powered, with the magnetic field then generated by the coil, the effect of the permanent magnets can be weakened or eliminated so that under the effect of the spring force, the friction coupling moves out of engagement, wherein the movable armature element leaves the force-fit position.
Such so-called fail-safe couplings are consequently held in a switched state due to the magnetic effect of permanent magnet means even when the electromagnet arrangement is not powered. The permanent magnet means are usually arranged in the manner of disks, for example, between two shells of the coil body. The magnetization direction of the permanent magnet means is axial in relation to the axis S about which the rotor rotates.
Because of their external dimensions, in particular in the direction radial to the rotor axis, the known friction switch couplings discussed have previously been unable to be used for all desired application possibilities, or can only be used when sufficient radial construction space is available.